Re: [HACKERS] COPY FROM STDIN behaviour on end-of-file

Thomas Munro <thomas.munro@enterprisedb.com> writes:
> On Tue, May 16, 2017 at 6:29 PM, Vaishnavi Prabakaran
> <vaishnaviprabakaran@gmail.com> wrote:
>> Hi, I could not reproduce this issue. Even after Ctrl+d , subsequent COPY
>> from commands reads the input properly. Is there any specific step you
>> followed or can you share the sample testcase?

> Hmm.  Doesn't happen on GNU/Linux, does happen on macOS and FreeBSD.

Hah, confirmed here.  Thinking about it, it seems like glibc must be
exceeding its authority to make this work on Linux; I don't know of
anything in POSIX saying that the eof indicator should go away without
a clearerr() call.  In fact, it seems like glibc is violating its own
documentation --- "man feof" saith
      The function feof() tests the  end-of-file  indicator  for  the  stream      pointed to by stream, returning
non-zeroif it is set.  The end-of-file      indicator can only be cleared by the function clearerr().
 

I had been supposing that this was a feature addition and should be left
for the next commitfest.  But given that it already works as-expected on
popular platform(s), the fact that it doesn't work the same on some other
platforms seems like a portability bug rather than a missing feature.
Now I'm inclined to treat it as a bug and back-patch.

Reviewing the actual patch, though ... there seem to be paths through
handleCopyIn that would not hit this, particularly the sigsetjmp path.
It's unlikely that we'd get control-C before we finish servicing
control-D, but maybe not impossible.  Wouldn't it be better just to do
an unconditional clear at the end, maybe
copyin_cleanup:
+    /* In case input is from a tty, reset the EOF indicator. */
+    clearerr(copystream);
+     /*     * Check command status and return to normal libpq state.     *

(I'd be inclined to make the comment significantly more verbose than
that, btw.)
        regards, tom lane